Add ckwnc to real-world uses

index.html

@@ -123,6 +123,7 @@
       <li><a href="http://sqlfiddle.com">SQLFiddle</a> (SQL playground)</li>
       <li><a href="http://tour.golang.org">Go language tour</a></li>
       <li><a href="http://cssdeck.com/">CSSDeck</a> (CSS showcase)</li>
+      <li><a href="http://www.ckwnc.com/">CKWNC</a> (UML editor)</li>
      </ul>
 
   </div></div>